In this lecture, we saw the technique used to track the camera movement in a scene and how to combine or premultiply several sequences.
In order to track the movement of a scene, we can add tracking points in Nuke that will detect the camera movement. This is a useful tool for rotoscoping since we will not have to adjust the roto in every single frame because of the camera shake. Sometimes it is important to add several tracking points as the camera movement will be different in the foreground, middleground, and background because of the motion parallax.
In another note, we can also combine several elements like rotos together in Nuke with a ‘merge’ node. However, it is important to keep in mind that the alpha channel value always has to be between 0.0 and 1.0. This can be sorted changing the way that the layers interact with each other, with settings like ‘screen’, ‘over’, ‘max’, etc. ‘Channel merge’ nods can also be used for this but they are not as reliable as the ‘merge’ nods.
When layering scenes, there is a tool that it is used in most of the cases called ‘Premult’. This tool premultiplies the RGB values by the alpha so the two layers are visible at the same time. It is also important to combine ‘Premult’ node with ‘Copy’ to add the alpha to the background.
The assignment this week was to rotoscope the bridge from the running man’s video and the mountain from the air balloon project using tracking points.
